Dedicated Tiresto Energy Facilities

Most facilities that burn tires or TDF use the rubber to supplement a primary fuel such as coal, gas, or waste wood. One company, however, the Oxford Energy Company, is operating two electric power plants using tires as the only fuel, and is planning several more.

3.1 INDUSTRY DESCRIPTION

Two dedicated tires-to-energy facilities, are currently operational in the United States: the Modesto Energy Project in Westley, California, and the Exter Energy Company in Sterling Connecticut. The Modesto Energy Project is a subsidiary of The Oxford Energy Company (Oxford Energy), which was founded in 1985, and is the only commercially operating electric power plant using only tires for fuel. The plant, which cost about $40 million to build, has a potential generating capacity of 15.4 megawatts (MW) of electricity per year and an actual capacity of 14.5 MW.1 It was designed specifically to burn whole scrap tires as its sole fuel. Although tire-derived fuels have been tried on a smaller scale elsewhere in the world, the Modesto Energy Project is apparently the first to operate successfully on a large scale.2

The location of the Modesto Energy Project is directly adjacent to the country's largest tire pile, which contained at its maximum, somewhere between 30 and 40 million tires. The tires in this pile are piled up to 40 feet high, and initially covered a canyon 1/4 mile wide for about a mile in distance.1

The technology used for the Modesto Energy Project was developed and licensed by the German company Gummi-Mayer in the late 1970's. The prototype facility on which Modesto was based has been operating successfully since 1973,3 but is only generating about 1 to 2 MW. Oxford Energy has exclusive licensing rights for the technology for the entire United States.4

In August 1991, Oxford Energy began start-up operations of another dedicated tires-to-energy electric power plant, called The Exeter Energy Company. Exeter, located in Sterling, Connecticut, is a $100 million, 30 MW facility, which is twice as large as the Modesto Energy Project.1 When commercial operation begins, power will be sold to Connecticut Light and Power.5 No tire pile exists near the Connecticut site, and Exter Energy Company uses a tire collection system. A tire sorting center will be located in Plainfield, Connecticut. The boilers can combust both whole and shredded tires.6 An anticipated 10 million tires per year will be used.1 The facility is anticipated to produce a greater cash flow than the Modesto Energy Project because all tires will come from the "flow", generating greater tire tipping fees; the fuel feed system is less complicated (no 420-foot incline is needed); and the same size workforce is used in generating twice the amount of electricity.1

Oxford Energy has also announced plans to build the Erie Energy Project, to be located in Lackawanna, New York. This facility is a 30 MW, 10 million tire/yr, plant that is in the last stages of planning for construction. The plant is planned to be constructed in an Economic Development Zone, which gives tax benefits to the company. Power sales will be to New York State Electric and Gas. Construction is anticipated to begin by the late 1991, with operation beginning in 1993. The plant will not be required to obtain a PSD permit, and a draft air permit and draft EIS have been submitted.1

A fourth facility, the Moapa Energy Project, is planned for construction in Moapa, Nevada, about 50 miles northeast of Las Vegas. The plant would require 15 million tires per year to generate 49 MW per hour, and would sell power to Nevada Power. The environmental impact statement and air emissions permits for this facility have been accepted, and public hearings are upcoming. Construction may begin in 1992, with operation commencing in 1993.1

3.2 PROCESS DESCRIPTION

This section of the report describes the process used at the Modesto Energy Project.

Tires for the boilers are obtained from the adjacent tire pile and from the community. Altogether, about 4.5 million tires per year are burnedI The Modesto Energy Project is required to obtain about half of these tires from the existing tire pile, and is permitted to acquire about half of its fuel from the community (referred to as the "flow"). For example, 2.6 of the 4.8 million tires burned in 1990 at the facility were from the "flow." This arrangement exists to balance the need to reduce the size of the hazardous tire pile with the desire of the company to obtain the most economical source possible of tires. Oxford Energy currently (1991) pays about $0.25 per tire for tires from the tire pile, but receives money for each tire acquired from the flow. The size of the tire pile will be decreased until a tire reserve remains of about 4 million tires.1

Modesto has created a subsidiary, Oxford Tire and Recycle, to collect and transport tires from tire dealers. The company sorts the tires to remove good used tires for resale for recapping or retreading. The remaining scrap tires (approximately 80 percent) are fed whole to the boilers.1

3.2.1 General Operation

The facility consists of two whole-tire boilers that together generate 125,000 pounds per hour of 930 psig steam.6 The output steam of the 80-foot high boilers combines to drive a 15.4 MW General Electric steam turbine generator. Figure 3-1 provides a schematic of the process flow at Oxford.

Tires acquired from the "flow" are stored in a specially designated area near the existing tire pile. The tires are fed into a hopper located adjacent to the tire pile. An automated tire feed system singulates tires (spaces them individually) up to 800 tires per hour, to a conveyor belt traveling 420 feet up a hill to the power plant. Tire feed rate averages 350 to 400 tires per hour to each boiler.1

The boilers and feed system can accommodate tires made of rubber, fiberglass, polyester, and nylon, and as large as 4 feet in diameter. Tires larger than four feet must be chipped or used in other ways. Assuming each tire weighs about 20 pounds, total weight of the tires fed to each boiler is about 7,000 to 8,000 lbs per hour. (Total energy input is estimated to be 190 million (MM) Btu's.1) Tires are weighed by automated scales and information is fed to the computer to facilitate appropriate tire feed to the boilers. Tires are fed onto the grate in the combustion chamber located at the bottom of one of the two 80-foot high boilers. The 430 square-foot reciprocating stoker grates are composed of several thousand steel bars made of a stainless steel alloy to prevent slag from adhering to the metal.1 This prevents plugging of the air distribution system by viscous liquids resulting from tire combustion. The grate configuration allows air flow above and below the tires, wnich aids in complete combustion. The bars resemble a series of steps sloping downward that move back and forth,

Feed Hopper

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